The present invention relates to continuous hot rolling methods and systems therefor and, more particularly, to a continuous hot rolling method and a system therefor for joining a plurality of hot materials to be rolled to each other to conduct hot rolling continuously, as well as a method of and apparatus for joining a plurality of hot materials to be rolled to each other in a continuous hot rolling system.
Normally, a hot rolling system comprises a continuous casting machine, a heating furnace, a plurality of rough rolling mills and a plurality of fine rolling mills. Hot steel webs manufactured by the continuous casting machine successively pass through a heating step at the heating furnace and a hot rolling step at the rough rolling mills and the fine rolling mills. Thus, the hot steel webs are brought respectively to products. The hot steel webs are processed as slabs at the heating step and, accordingly, are rolled intermittently one by one at the hot rolling step.
In the hot rolling, continuous rolling has been considered in place of the intermittent rolling. The continuous rolling is made possible if hot materials to be rolled (hereinafter referred simply to as "hot materials" or "material"), before rolling or during, can be joined to each other. If the continuous rolling is made possible, extremely large profits or advantages can be expected such as saving-energy, an improvement in yield, power-saving and the like, in addition to an improvement in productivity. For this reason, various methods of joining the hot materials to each other have been proposed until now. For example, a joining method, in which adjacent joining surfaces are welded to each other by high frequency induction heating, is disclosed in JP,A,60-170581 and JP,A,62-234679. A joining method, in which arc is generated by direct current to weld adjacent joining surfaces to each other, is disclosed in JP,A,61-253178. Further, JP,A,62-127185 discloses a method in which iron powder is mixed, if necessary, with oxygen gas to heat and dissolve adjacent joining surfaces and to blow out oxidized scale from the joining surfaces, and then the joining surfaces are joined under pressure to each other.
However, any of the above-described prior art is insufficient to secure that the adjacent hot materials are joined to each other, and continuous rolling has not yet been put into practical use. The reason for this is as follows. That is, as will be described later, reliable joining of the adjacent hot materials requires three conditions including 1 heating the entire adjacent end surfaces or the entire adjacent joining surfaces of the respective materials, to sufficient temperature equal to or above about 1400.degree. C., 2 no existence of oxidized scale on the adjacent joining surfaces more than a limit amount for joining, and 3 evenness or flatness of the configuration of the adjacent joining surfaces as far as possible. However, the prior art does not satisfy these conditions.
Specifically, of the above-described prior art, JP,A,62-127185 contemplates the aforesaid point 2 of removal of oxidized scale. In JP,A,62-127185, however, oxygen gas is merely abutted against the adjacent joining surfaces with reference to the condition 1, and it is impossible to heat the entire adjacent joining surfaces to temperatures sufficient to facilitate joining. Also in the joining method due to the high frequency induction heating and the joining method due to the arc, it is difficult to put to practical use since large equipment is required to sufficiently heat a central portion of each of the adjacent joining surfaces and the oxidized scale affects the joining.
Moreover, no consideration is made in any of the above-described prior art with reference to the point 3. Specifically, adjacent end surfaces of the respective hot materials to be joined to each other are generally sheared by a drum-type shear so that each of the sheared surfaces is not brought to a surface straight in a thickness-wise direction and in a widthwise direction, but is brought to an irregular or uneven configuration. For this reason, mere heating and joining of the end surfaces to each other as they are make it impossible for the entire adjacent end surfaces of the respective materials to be joined to each other, but local joining is often liable to occur. Such local joining will cause an accident such as cutting or severing of the materials since tension is loaded onto the materials during rolling.
Further, a large thrust force is required for avoiding the local joining, but in this case, difficulties will occur such that large swelling or bulge is produced at the joined portions, the hot materials are joined to each other under a bent condition, and the like. Thus, a problem will occur in rolling after joining.
Furthermore, as another prior art relating to the continuous hot rolling system, JP,A,59-130603 has proposed that, on an inlet side of rough rolling mills or fine rolling mills in a hot rolling line, a trailing end of a preceding hot material and a leading end of an adjacent succeeding hot material are reduced in thickness by a press and, subsequently, both the thickness-reduced ends are joined to each other, thereby continuing the hot materials to be rolled.
In the above-described prior art, however, no consideration is made to problems during the rolling step after the hot materials have been reduced in thickness by a press tool. Thus, there are the following problems.
Specifically, since the trailing end of the preceding material and the leading end of the succeeding material are free, forcing due to the press tool will cause irregularities to be formed on the trailing and leading end surfaces. Thus, if the trailing and leading end surfaces are joined to each other, it is impossible to sufficiently join the end surfaces to each other. That is, the aforesaid condition 3 is not satisfied. Furthermore, in JP,A, 59-130603, it has been proposed that the irregularities on the end surfaces after pressing are crop-cut by a shear, and the end surfaces are reshaped. As described previously, however, a surface sheared by the drum-type shear is not brought to one straight in the thickness-wise direction and in the widthwise direction. Moreover, since the exclusive shear is required to be arranged, the system is complicated in structure. Further, since the joining is conducted by normal butt welding, considerable time will be required for press operation or working with respect to the ends of the materials and the joining operation with respect to the ends of the adjacent materials. This reduces the productivity and largely reduces the temperature of the entire hot materials. Furthermore, there is also the problem that since the joining time is long, a looper having large capacity will be required to practice continuous running or operation.
It is therefore a first object of the invention to provide a method of and an apparatus for joining hot materials to be rolled to each other as well as a continuous hot rolling system, in which conditions including heating of joining surfaces to adequate temperature, removal of oxidized scale, and an improvement in flatness of the joining surfaces are all satisfied to secure joining of the materials to each other thereby enabling continuous rolling.
It is a second object of the invention to provide a method of joining hot materials to be rolled to each other as well as a continuous hot rolling method and a system therefor, in which a trailing end of a preceding hot material and a leading end of an adjacent succeeding material are reduced in thickness by a press without occurrence of deformation on trailing and leading end surfaces due to the press, to secure that the trailing and leading ends of the respective hot materials are joined to each other for a short period of time.